Optics and Ophthalmology

Sources

Vision and Light . Closely related to mathematics and physics, the field of optics attempts to answer questions of what and how people see. By reflecting on what people see, Muslim scientists delved into the realm of philosophy and religion. People in several faith traditions have questioned whether the physical world is actual reality or some sort of unreal entity that veils the reality of God. While Muslims joined other traditions in that debate, they also made enormous strides in discovering how vision works. Optics also looks at the physical properties of light, examining questions about what makes a rainbow or why images look distorted when reflected on a convex or concave surface as opposed to a flat one. Mathematics and physics were the tools needed to answer these questions.

The Father of Modern Optics . While earlier Muslim scholars also studied modern optics, they mostly accepted Greek sources—especially Aristotle, Ptolemy, and Euclid—including their claim that vision shoots from the eyes. Aristotle in particular had written that the eyes send out rays of light that illuminate the objects one sees. In the eleventh century, however, the Muslim scholar Ibn al-Haytham (called Alhazen in the West) did research in Egypt and Spain that led him to reach conclusions about

the nature of light and vision that contradicted the teachings of the Greeks and earned him the title “Father of Modern Optics.” Ibn al-Haytham discovered that the eyes receive reflected light from objects, rather than emitting it. He thus established the true scientific basis for vision. The next step was to understand the nature of light and how the eye transforms light into vision. Ibn al-Haytham devoted virtually all his adult life to sophisticated experiments designed to answer some of these questions.

The Nature of Light . Ibn al-Haytham and the Muslim scientists contributed much to the understanding of the nature of refracted light. Ibn al-Haytham wrote about what happened to light when it passed through clear substances such as water, air, and glass. He also did experiments on the dispersion of white light into the colors of the spectrum and was thus able to explain how light traveling through the atmosphere can create a rainbow. These studies led him to other discoveries about the atmosphere. He found that it becomes less dense at higher elevations and thus refracts light in different ways. By discovering that twilight begins when the sun is nineteen degrees below the horizon, he was able to calculate the thickness of the earth’s atmosphere. He wrote an entire book describing how various atmospheric conditions create different colors of a sunset. Ibn al-Haytham’s works on light and on mirrors and their reflective qualities had a strong influence on Renaissance artists and architects, who were trying to understand the concept of perspective and how to reproduce on canvas the visual effect of three-dimensional space.

The Human Eye . Ibn al-Haytham drew diagrams of how vision enters the eye through light that is reflected or refracted off of physical objects. He was the first scientist to put forth the theory that vision is the result of the workings of the eye, the optic nerve, and the brain. These studies influenced the works of Roger Bacon and Leonardo da Vinci. Another Muslim scholar, al-Zahrawi, had done extensive studies of the eye in the tenth and early eleventh centuries, writing texts on eye surgery and describing how he had removed cataracts by siphoning them out of the eye with a hollow needle. The eleventh-century physician Ibn Sina (Avicenna in Latin) was the first scientist to describe the anatomy of the eye in great detail, identifying parts such as the cornea, iris, retina, layer lens, the inner water, the optic nerve, and the optic chiasma that conducts the optic nerves to the brain.

Sources

Seyyed Hossein Nasr, Islamic Science: An Illustrated Study (London: World of Islam Festival Publishing, 1976).

Nasr, Science and Civilization in Islam (Cambridge, Mass.: Harvard University Press, 1968).